Tohatsu 6hp four stroke - No Spark

[Ciaobella]

Hi, I am new to this forum, I have had a good sniff around to try to find a similar thread but couldn't find one so please excuse me if I am going over old ground
I recently bought a second hand Tohatsu 6hp in a hurry as my old Suzuki gave up while out in the English Channel, when it was delivered it struggled to start. I assumed this was due to stale petrol. I changed the fuel and eventually it started and ran well. That was the last time it ran.
I spent a day checking the ignition system, however with black box's it's hard to check stuff with out specific equipment.
I changed the plug, overrode the deadman switch, and checked all the connectors then sprayed everything liberally with WD40. Still no spark
I used an oscilloscope to check the output of the CDI to the coil, this peaked at about 30V and should be about 150V.
For the blog entry showing how I measured this goto
http://h20-ciaobella.blogspot.com/2011/11/annoying-jobs.html
I guess my questions are:
[/LIST]
Do CDi's generally breakdown, they are expensive and I don't want to swap it out only to find that this isn't the poblem.

• Can anything else cause the CDI to fail?
• If I find someone local with a similar engine, will I be able to swap the CDI to see if the fault shifts without risking someone elses CDI unit?
  
  Thanks in advance - Any help gratefully accepted.

 

[pvanv]

Re: Tohatsu 6hp four stroke - No Spark

In our shop here in the States, we test the ignition components with a good analog ohm meter. You can't trust a digital unit, because it may not provide enough drive to the circuit under test. Low primary voltage could be a bad CD, or, in the case of the early-style model MFS6A2 (which yours appears to be), it could be a bad exciter or pulser... Or for that matter, an ignition coil that is starting to fail. Did you measure the output from the CD with the coil disconnected? To rule out a leaky deadman kill switch, just disconnect it (it grounds out the ignition to kill it). We would normally just connect the plug to the HT lead, and hand hold it to the block to observe the spark, which should be a strong blue.

You will want to check resistance to ground of the coil primary (where the CD feeds the pulse), the HT lead (coil secondary), and also the inputs to and output from the CD box, as well as across the exciter and pulser. Take readings with the components disconnected from each other.

If you do indeed diagnose a bad CD, the US part number and pricing are 3R1060601M C.D. IGNITION UNIT (CU2568) NEW STYLE $118.97.

 

[Ciaobella]

Re: Tohatsu 6hp four stroke - No Spark

Hi, sorry for the massive delay in replying. By thetime I'd fixed it I couldn't remember where I'd posted )
It turned out to be the exciter coil. The resistance was about half of what it should have been. Although it had a spark it wasn't man enough. The new exciter was a doddle to fit and the engine has been fantastic all this season.
Many thanks
Phil